Touch detection circuit with different charging and discharging currents and operating method thereof

Abstract

There is provided a touch detection circuit including a charging circuit, a discharging circuit, a counter and a processor. The charging circuit charges a detection capacitor within a charging interval using different currents. The discharging circuit discharges the detection capacitor within a discharging interval using different currents. The counter counts the charging interval and the discharging interval. The processor subtracts a baseline time from a counted charging time and a counted discharging time to cancel the noise interference.

What is claimed is: 
     
       1. A touch detection circuit, comprising:
 a detection capacitor, configured to generate a capacitor voltage; 
 a charging circuit, configured to charge the detection capacitor within a first charging interval using a first charging current, and charge the detection capacitor within a second charging interval using a second charging current smaller than the first charging current; 
 a discharging circuit, configured to discharge the detection capacitor within a first discharging interval using a first discharging current, and discharge the detection capacitor within a second discharging interval using a second discharging current smaller than the first discharging current; 
 a counter, configured to sequentially count the first charging interval, the second charging interval, the first discharging interval and the second discharging interval as a detection cycle; and 
 a processor, configured to identify a touch event according to the second charging interval and the second discharging interval without according to the first charging interval and the first discharging interval. 
 
     
     
       2. The touch detection circuit as claimed in  claim 1 , further comprising a comparing circuit, wherein the comparing circuit is configured to compare the capacitor voltage with a first reference voltage and a second reference voltage for conducting the charging circuit to the detection capacitor or conducting the discharging circuit to the detection capacitor. 
     
     
       3. The touch detection circuit as claimed in  claim 2 , wherein the charging circuit and the discharging circuit respectively comprise a variable current source and a switching element, and the processor is further configured to
 control the variable current source and the switching element of the charging circuit to cause the second charging interval to be larger than the first charging interval, and 
 control the variable current source and the switching element of the discharging circuit to cause the second discharging interval to be larger than the first discharging interval. 
 
     
     
       4. The touch detection circuit as claimed in  claim 3 , wherein within the detection cycle,
 the first charging interval is prior to the second charging interval, and 
 the first discharging interval is prior to the second discharging interval. 
 
     
     
       5. The touch detection circuit as claimed in  claim 1 , wherein the processor is further configured to change the first charging current and the first discharging current to alter the detection cycle when the detection cycle is equal to a noise cycle. 
     
     
       6. The touch detection circuit as claimed in  claim 5 , wherein
 the charging circuit and the discharging circuit respectively comprise multiple current sources and multiple current switches, and 
 the processor is configured to change the first charging current and the first discharging current by changing conducting states between the multiple current sources and multiple current switches. 
 
     
     
       7. The touch detection circuit as claimed in  claim 1 , wherein when a variation of a summation of the second charging interval and the second discharging interval between successive detection cycles is larger than a variation threshold, the processor identifies occurrence of the touch event. 
     
     
       8. A capacitive switch, comprising:
 a detection capacitor, configured to generate a capacitor voltage; 
 a charging circuit, configured to charge the detection capacitor sequentially using a first charging current and a second charging current, smaller than the first charging current, within a charging interval; 
 a discharging circuit, configured to discharge the detection capacitor sequentially using a first discharging current and a second discharging current, smaller than the first discharging current, within a discharging interval; 
 a counter, configured to sequentially count the charging interval and the discharging interval as a detection cycle; and 
 a processor, configured to subtract a charging reference time and a discharging reference time from the detection cycle to generate a time of interest, and output a control signal according to a variation of the time of interest between successive detection cycles. 
 
     
     
       9. The capacitive switch as claimed in  claim 8 , wherein the processor is configured to
 control the charging circuit to charge the detection capacitor within the charging reference time using the first charging current, and 
 control the discharging circuit to discharge the detection capacitor within the discharging reference time using the first discharging current. 
 
     
     
       10. The capacitive switch as claimed in  claim 9 , further comprising a comparing circuit, wherein the comparing circuit is configured to compare the capacitor voltage with a first reference voltage and a second reference voltage for conducting the charging circuit to the detection capacitor or conducting the discharging circuit to the detection capacitor. 
     
     
       11. The capacitive switch as claimed in  claim 10 , wherein the charging circuit and the discharging circuit respectively comprise a switching element, and the processor is further configured to
 control the switching element of the charging circuit to cause the charging reference time to be smaller than a half of the charging interval, and 
 control the switching element of the discharging circuit to cause the discharging reference time to be smaller than a half of the discharging interval. 
 
     
     
       12. The capacitive switch as claimed in  claim 8 , wherein the processor is further configured to change the first charging current and the first discharging current to alter the detection cycle when the detection cycle is equal to a noise cycle. 
     
     
       13. The capacitive switch as claimed in  claim 12 , wherein
 the charging circuit and the discharging circuit respectively comprise multiple current sources and multiple current switches, and 
 the processor is configured to change the first charging current and the first discharging current by changing conducting states between the multiple current sources and multiple current switches. 
 
     
     
       14. An operating method of a touch detection circuit, the touch detection circuit comprising a detection capacitor, a charging circuit, a discharging circuit and a counter, the operating method comprising:
 charging, using the charging circuit, the detection capacitor using a first charging current, and counting a first charging interval using the counter; 
 charging, using the charging circuit, the detection capacitor using a second charging current, smaller than the first charging current, and counting a second charging interval using the counter; 
 discharging, using the discharging circuit, the detection capacitor using a first discharging current, and counting a first discharging interval using the counter; 
 discharging, using the discharging circuit, the detection capacitor using a second discharging current, smaller than the first discharging current, and counting a second discharging interval using the counter; and 
 identifying a touch event according to a time variation of multiple summations of the second charging interval and the second discharging interval. 
 
     
     
       15. The operating method as claimed in  claim 14 , wherein the first charging interval and the first discharging interval are not configured to identify the touch event. 
     
     
       16. The operating method as claimed in  claim 14 , wherein the touch detection circuit further comprises a comparing circuit, and the operating method further comprises:
 comparing, using the comparing circuit, a capacitor voltage of the detection capacitor with a first reference voltage and a second reference voltage to determine whether to charge or discharge the detection capacitor. 
 
     
     
       17. The operating method as claimed in  claim 14 , wherein the charging circuit and the discharging circuit respectively comprise a variable current source and a switching element, and the operating method further comprises:
 controlling the variable current source and the switching element of the charging circuit to cause the second charging interval to be larger than the first charging interval; and 
 controlling the variable current source and the switching element of the discharging circuit to cause the second discharging interval to be larger than the first discharging interval. 
 
     
     
       18. The operating method as claimed in  claim 14 , wherein the first charging interval, the second charging interval, the first discharging interval and the second discharging interval form a detection cycle, and the operating method further comprises:
 changing the first charging current and the first discharging current to alter the detection cycle when the detection cycle is equal to a noise cycle. 
 
     
     
       19. The operating method as claimed in  claim 18 , wherein the charging circuit and the discharging circuit respectively comprise multiple current sources and multiple current switches, and the operating method further comprises:
 changing conducting states between the multiple current sources and the multiple current switches to alter the first charging current and the first discharging current.